Not applicable.
The invention relates to the field of heat sealing caps to containers. In particular, the invention is an adjustable sealing head for an inductive cap sealing apparatus.
Inductive sealing is a well-known method for hermetically sealing the openings of containers. Inductive sealing requires an electromagnetic-field-producing apparatus and a foil-polymer seal. Typically, the apparatus includes at least one coil of wire wound to produce an electromagnetic field when electric current is supplied to the coil. It is well-known in the art that electromagnetic fields induce eddy currents within metal, which in turn heat the metal. The seal comprises a thin layer of aluminum foil onto which is laminated a polymer layer that is molecularly compatible with the container to be sealed. When the seal is placed onto the container and the container is placed within an electromagnetic field, the eddy currents in the foil give off energy in the form of heat, which melts the polymer layer. Removing the seal from the electromagnetic field allows the polymer to cool and molecularly fuse with the container to create an airtight seal. U.S. Pat. No. 6,153,864, assigned to the assignee of the present invention and hereby incorporated by reference, discloses an example of an inductive sealing apparatus using this technique.
Typically, containers to be sealed ride along on conveyers beneath one or more sealing heads. The sealing heads can be fixed in place or indexed in a rotary carriage. Multi-headed cap sealers typically provide higher sealing rates than single-headed cap sealers. In both cases, however, it is important for the sealing head to provide an appropriate magnitude of magnetic flux in the area of the container top. Too much flux can melt the container or weld the foil seal to the container such that it is difficult to remove. Too little flux will not adequately seal the container.
Typical inductive sealing apparatuses have an adjustable mounting frame to properly position the sealing head with respect to containers being sealed. Such an adjustment is usually adequate for cap seals with a single sealing head. However, slight differences in the coil winding and loop isolation of multiple sealing heads can cause variances in the magnetic flux at the container top. Thus, adjusting the head mounting frame does not correct for magnetic flux variations between the heads of a multi-headed cap sealer, which can result in inconsistent sealing of the containers.
Accordingly, there is a need in the art for an adjustable sealing head that can be used in a multi-headed cap sealer to compensate for magnetic flux variations between multiple sealing heads.
The present invention provides an adjustable sealing head for use with an inductive sealing apparatus. The sealing head includes a housing defining a cavity that is disposed about and extends along a central axis. A coil bobbin disposed in the housing cavity has a cylindrical support extending along the central axis about which a wire coil capable of producing a magnetic field when energized is wound. An adjustment mechanism attaches the coil bobbin to the housing and enables manual adjustment of the coil bobbin in the axial direction with respect to the housing.
In one preferred form, the coil bobbin is adjustably fastened to a cap plate fixed at one of the housing. Rotating the fasteners allows the coil bobbin to be axially repositioned with respect to the housing.
In one preferred form, the inner housing is adjustably mounted at its top to a radial member fixed to the housing in the central cavity. Rotating fasteners threaded into the radial member moves the coil bobbin axially with respect to the housing. Preferably, the cylindrical wall of the housing includes a pair of axial apertures housing a pair of spring and push rod assemblies mounting a lower cap plate. The spring and rod assemblies bias the cap plate away from housing so that the cap plate can clamp the cap and/or seal against a container being sealed placed beneath the sealing head.
In yet another preferred form, the sealing head is includes a magnetic isolator disposed within the cylindrical support about which the wire coil is wound. The magnetic isolator is contained in an isolator housing have an externally threaded end that engages a threaded bore in a radial member fixed to the housing or part of the movable coil bobbin. Rotating the isolator housing changes its axial position with respect to the coil bobbin so as to alter the magnetic flux lines produced by the wire coil when energized
The invention thus provides a sealing head for an inductive cap sealer that can be adjusted with respect to its mounting frame. The magnetic flux at the opening of the container being sealed can be adjusted by changing the position of the coil with respect to the container. The magnetic flux can also be adjusted by changing the position of the coil with respect to a loop isolation element. The sealing head is particularly suitable for use with multi-headed cap sealers because each sealing head can be independently adjusted to provide consistent magnetic flux of the all the sealing heads despite slight variation in mounting location and sealing characteristics of each sealing head. Proper sealing is further ensured by the spring loading the cap plate to clamp the cap and/or the inner seal against the container being sealed.
The foregoing and other objects and advantages of the present invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof and in which there is shown by way of illustration a preferred embodiment of the invention. Such an embodiment does not necessarily represent the full scope of the invention, however, a reference must be made therefore to the claims for interpreting the scope of the invention.